The overall objective of this proposal is to provide new information regarding the signal transduction pathways initiated by mechanical stimuli and leading to DNA synthesis in cultured vascular smooth muscle cells. This goal will be achieved by addressing three specific aims. In the first aim, the contribution of c-fos protooncogene to the mitogenic effect of cyclic stretching will be examined. It has been shown that cyclic stretching induces an increase in c-fos mRNA levels. It will be determined (a) if this increase is due to induction of transcriptional activation and/or (b) to an increase in c-fos mRNA half life, and (c) if there is a concomitant increase in c-Fos protein. The second aim will examine the mechanisms by which c-fos contributes to DNA synthesis induced by cyclic stretch. These experiments will investigate (a) if the increase in c-fos results in an increase in AP-1 activity and AP-1 binding to DNA, and (b) if increased AP-1 activity is required for DNA synthesis. Experiments in the third aim will determine if protein kinase C (PKC) activation is involved in the cellular response to cyclic stretching. This will be accomplished by analyzing (a) if cyclic stretching increases diacyglycerol levels, (b) if cyclic stretch activates PKC, (c) if PKC inhibition suppresses stretch-induced DNA synthesis and c-fos expression and (d) if PKC stimulation is able to induce c-fos expression in the experimental model. A final set of experiments will determine if Raf-kinase and MAP-kinase are activated in response to cyclic stretch through a PKC mediated mechanism. Taken together, these studies will broaden our knowledge of the signal mechanisms in response to mechanical factors in vascular smooth muscle cells.